Recently, the connection ports with universal serial bus (USB) protocol are widely applicable to portable electronic products, e.g. cell phone and digital camera. When these portable electronic products are connected to the hub for use, several execution modes are performed for communication and each of execution modes consumes the current with different magnitude level wherein the supplying current is distributed to each port of the hub. For example, when an electronic product is connected to one port, its execution mode is fixed and the available supplying current is decreased if the more and more electronic products are added. Meanwhile, a new electronic product is put into another port and the consumed current of the electronic product is greater than the available supplying current, the electronic product cannot correctly operate. Even if the previous connected product is removed from the hub, the new product cannot still operate. It is required to remove the new product from the port and reconnect the new product. Such the situation is quite inconvenient since the supplying current corresponding to each port cannot be adjusted correctly.
Although external transformer can be used in the hub to increase the supplying current of the hub, the current from the transformer is limited due to cost consideration. Specifically, when the ports in the hub are increased, the transformer must provide more current for the ports. Therefore, the port amount of conventional hub for the electronic products is considerably limited. That is, since the supplying current of the ports cannot be adjusted, the electronic products lack the flexibility for the user. Consequently, there is a need to develop a novel power management to solve the aforementioned problems.